Path: utzoo!attcan!uunet!ncrlnk!ncr-sd!hp-sdd!hplabs!amdcad!diablo!phil
From: phil@diablo.amd.com (Phil Ngai)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Usable I/O Address range on the PC bus ...
Keywords: Limited to addresses up to 0x0400 only??
Message-ID: <23617@amdcad.AMD.COM>
Date: 22 Nov 88 19:41:13 GMT
References: <5065@whuts.ATT.COM> <4229@encore.UUCP> <1275@cfa.cfa.harvard.EDU> <23608@amdcad.AMD.COM> <1278@cfa.cfa.harvard.EDU>
Sender: news@amdcad.AMD.COM
Reply-To: phil@diablo.AMD.COM (Phil Ngai)
Organization: Advanced Micro Devices, Inc. Sunnyvale CA
Lines: 31

In article <1278@cfa.cfa.harvard.EDU> ward@cfa.harvard.EDU (Steve Ward) writes:
|Where we disasgree is in the meaningfulness, hazards, etc. of 16-bit
|decoding.  I say, if you do 16-bit decoding, you make it selectable
|to be able to choose several different address locations, and preferably
|many alternate locations.  My reason for this is because all it takes

Oh, that's what you're talking about! The concept of using a forever
fixed address is so repugnant to me that it never occurred to me that
anyone might think of using it. I assumed that you would allow the
byte in the range 0-400 to be selectable. 

|There is one point in your statement that I am a little unclear about.
|You seem to be saying "use 16-bit address decoding, but the decoded
|address(es) should be in the first 1K byte range of the 64K I/O
|address space."  If this is a correct understanding, what's the

I mean you have to pick a byte on the range 0-400 and make sure it
does not clash with anyone else in the system. Then you can claim
that byte and all its aliases for your own use.

|Of course, the REAL solution is to say the heck with I/O address
|space decoding entirely, and memory map everything somewhere in
|the upper area of the 1MB memory address space  :-)

From what I have seen, there's plenty of IO addresses compared to
the amount of free space within the 1 MB range.

--

Phil Ngai, phil@diablo.amd.com
{uunet,decwrl,ucbvax}!amdcad!phil